1. Field of the Invention
The present invention generally relates to a paper ejection device and an image forming apparatus.
2. Description of the Related Art
Certain types of image forming apparatuses, such as stencil printers, adopt a scheme for achieving fine alignment of paper ejected onto a paper output platform by maintaining a deflected profile (elastically bent form) of paper, in which paper end portions in a direction perpendicular to a paper conveying direction are at higher level than a center portion, when the paper is ejected.
For instance, there is adopted a scheme of creating such an elastically bent form using a suction conveying unit and maintaining the elastically bent form using wing-shaped paper ejection supports or the like arranged on side fences of a paper output platform.
For example, Japanese Laid-open Patent Publication No. 2006-306568 discloses a technique for achieving better ejected-paper alignment by configuring side fences in such a manner that spacing between top portions of the side fences is smaller than spacing between bottom portions. Japanese Laid-open Patent Publication No. 2002-179325 discloses a technique of setting spacing between spacing-adjustable side fences to be narrower than a paper width size by a predetermined amount. Japanese Laid-open Patent Publication No. 2000-118845 discloses a technique of decreasing positions of side fences when paper is not thick paper. This technique utilizes relationship with a result of paper thickness detection, but does not take relationship with print speed into account. Japanese Laid-open Patent Publication No. 10-001254 discloses a technique of setting spacing between side fences to be slightly wider or narrower than an actual paper size depending on type and thickness of the paper. Japanese Patent Document No. 3669604 discloses a scheme of automatically adjusting side fences and an end fence to paper size. Japanese Laid-open Patent Publication No. 2009-012397 discloses a control scheme of moving an end fence in a direction away from a paper exit according to a print speed.
However, to the inventor's knowledge, there is not provided a technique that takes relationship between positions of, or spacing between, side fences and a print speed into account. Accordingly, there remains an unsolved problem that an elastically bent form of paper cannot be maintained when high-speed printing is performed, which can result in poor alignment of ejected paper.
Therefore, it is desirable to provide a paper ejection device capable of maintaining an elastically bent form of paper even when high-speed printing is performed by taking relationship between positions of side fences and a print speed into account, thereby preventing poor ejected-paper alignment, and an image forming apparatus including the paper ejection device.